1. Field of the Invention
The present invention generally relates to flexible storage tanks, and more particularly to a flexible relocatable storage tank for flowable materials such as liquids and granular material.
2. Description of the Related Art
Conventional structures for relocatable and collapsible tanks utilize designs such as a pillow or bladder tank, available from Aero Tec Laboratories, Inc., N.J., U.S.A. and others, which consists of a bag made in the shape of a pillowcase using flexible material. When empty, the bag folds flat and may be rolled or folded for storage and shipment. The filling/discharge flange is integrated into the top panel of the material, and the storage volume is sealed at all times with a negligible air or vapor pocket. This conventional design is a formless package when folded for transport with no real strong confluence points to allow for lifting to load onto a transport. In larger sizes, it must be loaded onto a single stiff pallet to allow for lifting by a forklift or crane. One of the other drawbacks of this conventional design is that the pillow tank does not tolerate high site slopes, and requires relatively large site areas because the average depth of the stored liquid inside of the tank is low. Moreover, such tanks appear to be relatively expensive, and do not lend themselves to the storage of granular materials. Also, liquids stored in the pillow tanks, which are exposed to bright sunlight, get extremely hot. This is undesirable for fuels or potable water. In order to ameliorate this effect, a cover needs to protect the tank from the sun, which requires a considerable structure to span the overall exposed surface of the tank.
Another conventional design uses rigid tanks, which are built with rigid panels forming the sides, and often a rigid metal support frame. The loads imposed by the stored liquid or grain are carried directly by these panels. These tanks may have a plastic membrane liner; however, this is not structural, rather it is provided more for sealing purposes only. Such tanks usually require prepared unsloped sites.
Other conventional designs consist of flexible bags with an external frame, such as the type disclosed in U.S. Pat. No. D334,238 and issued to Spedini, further illustrated in FIG. 1 herein. These designs are used especially for above-ground swimming pools, and consist of a tank using a bag of strong flexible material supported by an external metal frame consisting of a rim in the horizontal plane, supported off the ground by a series of inclined metal posts. As shown in FIG. 1, the flexible bag is a structural member which carries the loads imposed by the weight of the peripheral liquid or grain to the rim of the tank, and hence to the ground via the supporting posts. The weight of the liquid/grain in the central area of the tank, where the fabric is in contact with the ground, is supported directly by the ground. This conventional design offers a highly portable, low weight tank, which can be quickly and easily installed and dismantled. However it suffers from the following disadvantages.
First, the external structure of the conventional fabric tank must be considerably over-designed for the chosen depth of the associated liquid/grain because for depths differing from the design depth, the rim and external posts of the tank are subjected to extra bending loads, as depicted in the illustration of the conventional design used in practice shown in FIG. 2. This is particularly critical for the posts, which are subjected to significant compression forces, because the applied bending significantly increases the tendency for the posts to buckle. A second disadvantage of the conventional design shown in FIGS. 1 and 2 is that for similar reasons related to the varying depths of the associated liquid/grain, the problem is exacerbated if the tank is to be used in an emergency or unprepared, sloping, or undulating ground. Typically, these conventional tanks are severely limited to a few degrees of slope. Thus, such designs with external frames are used primarily for aboveground swimming pools, where the water is typically at or close to design depth, and such designs have found no functional application in storage tanks, which of course, must accommodate a large range of depths.
Moreover, the conventional fabric tank designs use relatively light fabrics for the bag and several light rigid components for the external frame. However, it is really only suitable for applications which can accept an open liquid surface, thereby limiting its use to non-potable water. Moreover, these conventional designs do not easily accept other granular materials, nor do they tolerate more than minimal slopes, and the frame must be stiffened appreciably to cope with partially filled conditions.
Therefore, there is a need for a relocatable storage tank for flowable materials such as liquids and granular materials comprising a bag of flexible material and having a generally square, rectangular, or circular shape, resting on a solid surface, together with at least one central post which supports the upper portion of the bag, wherein the post aids in carrying the weight of the flowable materials to the ground, thereby reducing the associated mechanical tensions in the fabric of the flexible material. Moreover, there is a need for a larger flexible relocatable storage tank for flowable materials such as liquids and granular materials which can improve the ease of relocation of the stored materials, and which allows for the use of the storage tank in confined and sloping sites, especially for temporary and/or emergency situations.
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional storage tanks the present invention has been devised, and it is an object of the present invention to provide a structure for a relocatable storage tank for liquids and granular materials. It is another object of the present invention to provide a structure for a relocatable storage tank for liquids and granular materials which improves the ease of relocation of the tank, and to allow use of the tank in confined and on sloping sites, especially for temporary and emergency conditions. It is a further object of the present invention to allow for larger depths of storage for the stored liquids in the storage tank. Still another object of the present invention is to allow for filling, storage, and discharge of granular materials from the storage tank. Yet another object of the present invention is to collect and carry the peripheral liquid/granular loads in tension, and take these loads to the ground in compression in at least one internal support system.
In order to attain the objects suggested above, there is provided, according to one aspect of the invention, a storage tank for flowable material such as liquids and granular material, wherein the storage tank comprises a container of flexible material, wherein the flexible material comprises a base portion for engaging a supporting surface, and at least one supporting post system mounted over the base portion and supported by the supporting surface, wherein the flexible material extending upwardly from the base portion forms a side portion and an upper portion of the storage tank, and is secured to the supporting post system. Furthermore, the storage tank of the present invention is provided in multi-geometrical embodiments including generally square, rectangle, circular, and polygonal shapes. In an alternative embodiment, the storage tank comprises an upper cap positioned on the upper portion of the storage tank. In another alternative embodiment, the storage tank further comprises support cables attaching the supporting post system to the supporting surface.
Additionally, the supporting post is generally rigid. Also, in an alternative embodiment, the supporting post is generally solid. Alternatively, the supporting post is generally hollow. Also, the supporting post may be embodied as a float. In another embodiment, the at least one supporting post system comprises a plurality of supporting posts interconnected by a linking element. Still alternatively, the storage tank comprises an outer support fabric over the flexible material. Additionally, the storage tank may further comprise a covering sheet over the storage tank, embodied as a fly sheet for solar protection and slope stabilization. The fly sheet could also provide a cover from rain, snow, leaves, etc.
In an alternative embodiment, a storage tank for flowable material such as liquids and granular material comprises a container of flexible material, wherein the flexible material comprises a base portion for engaging a supporting surface, and at least one support system positioned over the base portion, wherein the flexible material extends upwardly from the base portion to form a side portion of the storage tank, and is secured to one of a support rim and the support system, wherein the support rim is positioned over the base portion. The support system comprises one of a post and a float. Moreover, the post may be either solid or hollow. In an alternative embodiment, the storage tank further comprises a plurality of cables attaching the support rim to the support system. Furthermore, in another embodiment, the at least one support system comprises a plurality of supports interconnected by a linking element. Alternatively, the storage tank comprises an outer support fabric over the flexible material. Additionally, the storage tank may further comprise a covering sheet over the storage tank, embodied as a fly sheet for solar protection and slope stabilization.
In another alternative embodiment, the present invention provides a storage tank for flowable material such as liquids and granular material, wherein the storage tank comprises a flexible bag having a side portion and an upper portion. The storage tank further comprises at least one support structure contained within the flexible bag, whereby the support structure is positioned below the upper portion of the flexible bag, wherein the flexible bag is secured to a supporting surface, and wherein the support structure is secured to the supporting surface. Additionally, the flexible bag extends upwardly from the supporting surface, and is secured to one of a support rim and the support structure, wherein the support rim is positioned below the upper portion of the flexible bag. Alternatively, the storage tank further comprises a plurality of cables attaching the support rim to the support structure. The support structure may be embodied as a post, which may be hollow or solid, or the support structure may be embodied as a float. Still alternatively, the at least one support structure comprises a plurality of supports interconnected by a linking element. In another embodiment, the storage tank further comprises an outer support fabric over the flexible material. Additionally, the storage tank may further comprise a covering sheet over the storage tank, embodied as a fly sheet for solar protection and slope stabilization.
The present invention overcomes the several disadvantages of the conventional designs. For example, the present invention provides for an essentially vertical storage of the tank when it is not in use (i.e., stored footprint is very small), without requiring accessory equipment. Also, the present invention is easily loadable and carried to site by a forklift, crane, etc., without requiring accessory lifting gear such as pallets or a carrying case. The present invention tolerates installation and filling on sloping sites. Moreover, on steep slopes (approximately 10 degree grade), the present invention can easily be made stable by utilizing simple guy ropes/cables attached to the central post and anchored to the high side of the site. Additionally, the present invention""s central post provides a support for a fly sheet for solar heating and UV protection at a low cost. In fact, it is feasible to use this fly sheet to create some shrapnel protection for military use.
Other advantages of the present invention are that the present design allows for larger depths of stored liquids than conventional flexible tanks, and hence smaller footprint areas for a given capacity, which is ideal at congested or restricted sites. Furthermore, the present design accommodates for filling, storage, and discharge of granular materials at lower production costs compared to traditional designs.